1. Technical Field
The present invention relates to a power amplifier, and more particularly, to a class-D power amplifier for use as an audio amplifier, and an amplification method thereof.
2. Discussion of the Related Art
In the past, class-A, class-B, and class-AB power amplifiers, which perform linear amplification, have been used as mainstream audio power amplifiers. Recently, however, there has been research conducted on class-D power amplifiers, which perform amplification by utilizing switching operations based on pulse width modulation (PWM). Research has shown that class-D power amplifiers have poor linearity and superior power efficiency as compared to class-A, class-B, and class-AB power amplifiers, which have superior linearity and poor power efficiency.
Switching operations based on PWM in class-D power amplifiers result in harmonic distortion caused by high-frequency components and oscillations. To overcome such harmonic distortion, negative feedback has been used in class-D power amplifiers. In addition, because an audio power amplifier is driven with high current, it has additional functions for protecting components in an initial state or an abnormal state, such as an over-current condition or a power-failure state. U.S. Pat. Nos. 5,805,020 and 6,420,930 disclose exemplary class-D power amplifiers using negative feedback.
In a conventional class-D power amplifier using negative feedback, a predetermined switch is opened in the initial state or the abnormal state and negative feedback looping is blocked, thereby preventing over-current from flowing through the load side, such as a speaker. Here, an integral control circuit or proportional integral control circuit is input with a finite error signal and reaches a saturation state. In the saturation state, the predetermined switch is closed and there is a negative feedback loop so that the class-D power amplifier enters a steady state after the initial state or exits from an abnormal state. Then, because the integral control circuit or proportional integral control circuit is in the saturation state, an output signal exhibits an unstable excessive response phenomenon while the class-D power amplifier reaches the steady state.
To remedy the unstable excessive response phenomenon, the conventional class-D power amplifier includes an output-blocking switch before the load side, which outputs the output signal to the load side after the excessive response phenomenon is removed, and then the class-D power amplifier reaches the steady state. The rated power of the output-blocking switch corresponds to power consumed by the entire amplifying system in the steady state, which results in high power consumption by the conventional class-D power amplifier.